Early drug use significantly increases the odds of developing a Substance Use Disorder (SUD), and risk is exacerbated among Children of Substance-abusing parents (COSs) for whom earlier initiation predicts faster escalation in drug use and more rapid initiation-to-disorder trajectories (Hussong & Bauer, 2008). This underscores the need to identify early risk mechanisms of intergenerational transmission of addiction. Research shows that parental substance use robustly predicts child emotion dysregulation which, in turn, predicts risk for youth substance use (Zucker et al., 2009). Thus, child emotion dysregulation may be a critical link in transmission of substance use risk across generations. In order to identify the highest-impact prevention targets most likely to minimize intergenerational transmission of addiction, it is imperative to understand the mechanism by which parental addiction compromises child emotion regulation, setting the foundation for substance use initiation and escalation later in adolescence. Among low-risk non-substance-using samples, parent emotion socialization (i.e., supportive / unsupportive reactions to child distress) is a unique predictor of child emotion regulation (Eisenberg et al., 2011). However, the field has been remiss because very little is known about parent emotion socialization behaviors among substance-using parents, or how it relates to child outcomes. Findings from the PI's program of research indicate that parent emotion socialization may be the critical link explaining the relationship between parental substance use and child emotion regulation; however, this risk process has not been examined longitudinally or in the context of predicting later substance use risk among youth. It also remains unclear if this mechanism unfolds among community parents and youth and is thus generalizable to the broader population. Thus, the current application will test these questions via secondary data analysis of an ongoing large-scale longitudinal study which employs a multimodal assessment strategy with 579 youth. It is hypothesized that parental drug use, parent emotion socialization, and child emotion regulation will uniquely influence one another over time (i.e., transactional effects). Furthermore, it is expected that more severe parental substance use will predict less supportive parent emotion socialization which, in turn, will predict poorer child emotion regulation as an early developmental risk pathway, ultimately predicting earlier substance use onset and faster escalation in use among youth. The impact of this study lies in testing parent emotion socialization as the critical link explaining the relationship between parental drug use and child emotion dysregulation over time. By focusing on this early risk mechanism preceding actual substance use onset, this longitudinal study will further examine if early risk processes involving emotion socialization and early emotion dysregulation predict distal substance use outcomes into adolescence. Results will inform public health efforts aimed at minimizing intergenerational transmission of addiction by identifying parent emotion socialization as a critical early prevention target.